Such coupling devices are used in many applications, for example in vehicles, in fixed installations and in various types of machine constructions. In most cases, the sealing function of the coupling device is essential as are also reliability, price and handling aspects, including time required for mounting.
Furthermore, continuously increased demands are placed on engines as to, for example, performance, environmental influence and life. In order to satisfy these requirements, it is therefore necessary for the control systems to have the current status of flow rates, temperatures etc. for gases and liquids in the engine. Such information in real time from different parts of an engine therefore makes it possible to optimise operation.
One example of wireless communication is disclosed in U.S. Pat. No. 6,649,829 which uses RFID technology (RFID=radio frequency identification). The sensors in said document are, however, relatively expensive and beside require direct connection to a power source, such as a battery. The exchange of batteries involves an extra operation and thus causes inconvenience for the user.
RFID can be resembled to “electronic bar codes”, but with the difference that the RFID tag (RFID transponder) need not be visible for reading. An RFID system usually comprises readers with antenna and a data carrier with the unique code. As a rule, the data carrier is encapsulated to optimally fit the application. The most common encapsulating materials are different types of plastic; proximity to metal shields the product and greatly affects the performance of the system. RFID systems are available with active and passive transponders.
An active transponder has a power source (battery) of its own to be able to perform reception and transmission, a common reading distance being about 10 m.
A passive RFID system can be described as a radio system for short distances. The transponder has no power source of its own but is operated with the power induced by the antenna. The reading distance is usually below 0.5 m. The reading distance is highly dependant on the output power of the reader, the antenna size in both reader and transponder and also the ambient conditions, where metal usually has a negative effect on performance.